Bioorthogonal chemical reactions are a powerful tool to investigate how various biological pathways operate. These transformations require a balance of reactivity in order to achieve the desired outcome without causing deleterious side reactions. The azide functionality has emerged as an excellent precursor for such transformations due to its compatibility with biological systems and the ease in which it can be incorporated. Recently, the Raines group developed a phosphinoester reagent that was capable of converting azides into diazo compounds under mild conditions in organic based solvent systems. The first goal is to synthesize a related phosphinoester that is able to function without the need of organic solvents. The water solubility and reactivity of the reagent will be systematically optimized to promote the desired transformation without allowing water or other functional groups present in biological systems to react. When the first goal has been realized, the next step will be to explore the reactivity of the resulting diazo compounds. Finally, with a thorough understanding of reactivity, the tests will be moved to a biological setting. The highly reactive diazo compounds will be used to covalently crosslink biomolecules to better understand their function. This is just one of many useful applications of this chemical transformation. The development of a reagent capable of producing highly reactive diazo compounds from biologically compatible azides under physiological conditions will have a significant impact on the field of chemical biology. PUBLIC HEALTH RELEVANCE: The proposed research involves developing a water soluble reagent capable of converting a relatively inert azide group into a highly reactive diazo group under physiological conditions. This will serve as a general tool in chemical biology to understand how various biological processes operate. In addition, a transformation of this caliber will have a significant impact in synthetic chemistry, a field always looking for selective methods to produce reactive functionality.